1. 解开；松开；打开
    If you undo something that is closed, tied, or held together, or if you undo the thing holding it, you loosen or remove the thing holding it.

    e.g. I managed secretly to undo a corner of the parcel...
           我悄悄地设法解开了包裹的一角。
    e.g. I undid the bottom two buttons of my yellow and grey shirt...
           我解开了自己黄灰相间的衬衫上最下面的两个纽扣。

2. 撤销；抵消；消除
    To undo something that has been done means to reverse its effect.

    e.g. A heavy-handed approach from the police could undo that good impression...
           警方采取高压手段可能会毁掉之前留下的好印象。
    e.g. She knew it would be difficult to undo the damage that had been done...
           她知道想要消除已经造成的损害是很难的。

3. 破坏；毁掉
    If a person, organization, or plan is undone by something, that thing causes their failure.

    e.g. They were undone by a goal from John Barnes...
           约翰·巴恩斯的一粒进球使他们落败。
    e.g. Macbeth is the story of a Scottish soldier who becomes king but is undone by his own ambition.
           《麦克白》讲述的是一个苏格兰士兵当上了国王，却毁于自己的野心。

4. see also: undoing;undone